1. Field of the Invention
The present invention relates to a foraminous filter useful for removing Total Reduced Sulfur compounds (TRS), especially H.sub.2 S and mercaptans, and other oxidizable constituents from gases, as well as to a method for preparing the filter. More particularly, the present invention relates to a foraminous filter having an active form of manganese dioxide impregnated therein as an oxidative absorbent for Total Reduced Sulfur compounds.
2. Description of the Prior Art
Various processes and absorbents have been proposed for reducing the content of sulfur compounds in gases. Most of these processes and absorbents relate to the large-scale removal of sulfur compounds from industrial gases and particularly pertain to the removal of sulfur oxides. Because of their substantial acidic character, these sulfur oxides are readily absorbed by alkaline absorbents, and can suitably be removed on an industrial scale. Unfortunately, these same absorbents are not generally satisfactory for removing a number of important industrial byproduct sulfur compounds such as hydrogen sulfide, mercaptans and other related organic sulfur containing compounds, since the acidic character of these compounds is generally much less pronounced. In fact, there presently is no process being used commercially for the large-scale removal of such sulfur compounds, particularly the mercaptans, from industrial gases.
In British Patent Specification No. 1,576,534 a process for removing hydrogen sulfide from a hot reducing gas is disclosed. The process uses an absorbent comprising a mixture of finely divided manganese oxide, i.e., manganese of oxidation state 2, and finely divided aluminum oxide. However, this patent does not disclose that the absorbent can remove mercaptans from gas streams.
U.S. Pat. No. 3,898,320 to Atsukawa uses a dry, powdered absorbent comprising a hydrated manganese oxide to remove sulfur oxides from gas streams. There is no indication that this absorbent can be used to remove H.sub.2 S or reduced organic sulfur compounds, particularly mercaptans. As described, the sulfur oxides in the gas react with the hydrated manganese oxide absorbent to produce manganese sulfate. The manganese sulfate is subsequently solubilized in water, converted to manganese hydroxide in the presence of ammonium hydroxide and is thereafter reconverted to the hydrated absorbent by oxidation with an oxygen-containing gas.
U.S. Pat. No. 3,492,083 to Lowicki, et al., describes a process for removing sulfur containing compounds such as sulfur oxides and including H.sub.2 S and organic sulfur compounds which employs a complex multicomponent absorbent. This absorbent includes a metal oxide, hydrated oxide or hydroxide or preferably mixtures thereof, for example, manganese dioxide and magnesium oxide, in combination with an alkali metal or alkaline earth metal oxide or hydroxide, for example, sodium hydroxide.
Because of the lack of any commercially viable process for the large-scale removal of reduced sulfur compounds such as H.sub.2 S and particularly mercaptans, residential and commercial communities in the proximity of industrial facilities such as kraft paper mills, sewage treatment plants, oil refineries and the like commonly are subjected to pollution from such sulfur compounds. This pollution is a particular nuisance since these compounds are extremely odorous, having an easily detected, pungent odor at low concentrations. In fact, although odor perception varies from one individual to another, based upon many factors, these compounds can sometimes be detected at concentrations as low as one part per billion (ppb). Moreover, although atmospheric conditions (e.g., wind and rain) often may dissipate the odor causing contaminants in the air outside of residential and commerical establishments, once such contaminants have diffused inside, the odors tend to remain for protracted periods.
It is an object of the present invention therefore to provide a filter useful for removing H.sub.2 S and organic sulfur-containing compounds, particularly mercaptans, from a gas, particularly air.
It is another object of this invention to provide a filter useful for removing the aforementioned sulfur compounds from air that can readily be adapted to residential and small commercial applications.
It is a further object of this invention to provide a process for preparing a filter useful for removing these sulfur compounds from a gas.
It is still an additional object of the present invention to provide a method for removing organic sulfur-containing compounds from a gas stream.